COST Cost Estimate.
C = COST(Hd) return a cost estimate C for the filter Hd. The cost
estimate contains the following fields:
NMULT : Number of multipliers*
(* excluding multiplications by 0,1,-1)
NADD : Number of adders
NSTATES : Number of states
MULTPERINPUTSAMPLE : Number of multiplications per input sample
ADDPERINPUTSAMPLE : Number of additions per input sample
返回值是一个元包,基本意思是这个滤波器要用多少个乘法器,多少个加法器,有多少个状态,信号采样频率等.是实际硬件资源的一个估计的一个函数